In this Hugo-winning classic, the oppressed colonists of the Moon, many the descendants of people who were transported there as prisoners (rather like the founding of the Australian colonies) have lost their patience with the tyranny and exploitation of their Earthside masters. They long for freedom, and decide to tell Earth to go mind its own business. However, Earth is not willing to let go so easily.

When push comes to shove, the Loonies (as the Moon-settlers call themselves) are willing to stand up and fight. Furthermore, they have a secret weapon -- a self-aware computer system known to only a few of the rebels.

However, this novel is not merely an action-adventure story about the overthrow of a tyrant. It is also a philosophical exploration of the meaning of personal responsibility and what people should expect of themselves and their government. A persistant theme throughout the novel is TANSTAAFL, which stands for "There ain't no such thing as a free lunch." This sums up the central theme of the book, that everything has some kind of price, whether it is paid in money or other things.